For diagnosis, treatment, or prevention of diseases at the genetic level, techniques for extracting nucleic acids from a biological specimen such as cells, bacterium, or viruses have recently been in wide use in association with the nucleic acid amplification techniques. The techniques for extracting nucleic acids from the biological specimen are also on demand in various fields of applications, such as customized drug development, forensic, detection of endocrine disruptors, and so forth.
An example of the conventional nucleic acid extraction techniques is a method of solubilizing a specimen including cells with SDS or proteinase K, modifying and removing proteins with phenol, and then purifying a nucleic acid. However, the phenol-based extraction method has a credibility problem because the phenol-based extraction method requires a number of steps, which takes a lot of time, and the efficiency of the nucleic acid extraction method greatly depends on the worker's experience and skills. To resolve this problem, a kit having silica or glass fiber that specifically combines with a nucleic acid has been recently used. The silica or glass fiber has a low combining ratio with proteins or cell metabolites, so it is possible to acquire a nucleic acid at a relatively high concentration. This method is advantageous because it is more convenient in comparison to the phenol-based method. But the method uses a chaotropic reagent or ethanol that strongly inhibits the enzyme reaction such as polymerization chain reaction (PCR) or the like and thus requires a complete removal of the substances, that is, the chaotropic reagent or ethanol, so it could be an onerous task and takes a longer time. Recently, International Publication No. WO 00/21973 discloses a method of directly purifying a nucleic acid with a filter. The method involves passing a specimen through the filter to retain cells adsorbed by the filter, dissolving the adsorbed cells, filtering the cells, and then washing and eluting the adsorbed nucleic acid. However, in order to obtain the nucleic acid after adsorbing the cells with the filter, the method further requires the selection of the filter depending on the type of the cells. Another disadvantage is that the devices used in this method are too large and complicated for the worker to use with ease.